1. Field of Invention
The present invention relates to a connector for a respiratory mask and a respiratory mask.
The invention has been developed primarily for use with a breathable gas supply apparatus in Continuous Positive Airway Pressure (CPAP) treatment of, for example, Obstructive Sleep Apnea (OSA) and other ventilatory assistance treatments, such as Non Invasive Positive Pressure Ventilation (NIPPV) and will be described hereinafter with reference to these applications. However, it will be appreciated that the invention is not limited to these particular fields of use and also finds application in, for example, assisted respiration, mechanical ventilation and the like.
2. General Background and Related Art
CPAP treatment is a common ameliorative treatment for breathing disorders including OSA. CPAP treatment, as described in U.S. Pat. No. 4,944,310, provides pressurized air or other breathable gas to the entrance of a patient""s airways at a pressure elevated above atmospheric pressure, typically in the range 3-20 cm H2O.
It is also known for the level of treatment pressure to vary during a period of treatment in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment, as described in U.S. Pat. No. 5,245,995.
NIPPV is another form of treatment for breathing disorders which can involve a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration.
In other NIPPV modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in the applicant""s international PCT patent application No. PCT/AU97/00631.
Typically, the ventilatory assistance for CPAP or NIPPV treatment is delivered to the patient by way of a respiratory, preferably nasal, mask. Alternatively, a mouth mask or full face mask can be used. In this specification any reference to a mask is to be understood as incorporating a reference to a nasal mask, mouth mask or full face mask, unless otherwise specifically indicated.
In this specification any reference to CPAP treatment is to be understood as embracing all of the above-described forms of ventilatory treatment or assistance.
Breathable gas supply apparatus broadly comprise a flow generator constituted by a continuous source of air or other breathable gas generally in the form of a blower driven by an electric motor. The electric motor driving the blower is typically controlled by a servo-controller under the control of a micro controller unit. A hospital piped supply can also be used. The gas supply is connected to a conduit or tube which, in turn, is connected to the patient""s mask which incorporates, or has in close proximity, a gas washout vent for venting exhaled gases to the atmosphere. The gas washout vent is sometimes referred to as a CO2 washout vent.
As CPAP and NIPPV treatments are normally administered while the patient is sleeping, minimization of the noise is desirable for both the comfort of the patient and any bed partner. The exhausting of exhaled gas to the atmosphere through the gas washout vent creates noise due to turbulence generated at a shear layer between the moving vented gases and the still atmospheric air.
It is also desirable to locate the vent as close as possible to the mask in a location which encourages a circulation of flow within the mask so as to eliminate exhaled CO2 through the vent and encourage inhalation of the supplied breathable gas. In this way, the retention of CO2 within the mask is minimized. Further, by increasing the venting efficiency in this manner, the overall gas outflow is minimized, thereby reducing the opportunity for noise production.
One approach to minimize the noise generated by the venting of the exhaled gas is to direct the gas along an exterior surface which is a smooth prolongation of an interior surface of the outlet of the gas washout vent. This reduces the interaction between the vented gas and the still atmospheric air and, thus, the noise generated.
An example of the above approach is the AeroClick vent produced by MAP which has an annular vent passage that directs the exhaled gases along an adjacent cylindrical section of equal exterior diameter to the interior diameter of the annular vent. The AeroClick vent suffers from several disadvantages. Firstly, the annular vent is incorporated into a swivel mechanism which requires a certain amount of play or clearance in order to rotate freely. This play allows the components forming the interior and exterior surfaces of the annular vent passage to become misaligned and the size of the vent outlet being decreased from optimum in some regions and increased from optimum in other regions. The decreased area regions increase by the velocity of the gas flowing therethrough which increases noise and can produce an unpleasant whistling effect. Secondly, the flow of the gas from the vent outlet to a state where its velocity is in substantial equilbrium with the atmosphere is interrupted by an external shoulder closely downstream of the vent outlet. The shoulder is provided to locate the gas supply conduit. The stresses in the flow caused by the shoulder lead to the generation of noise. Additionally, the flow path from the gas conduit into the vent outlet is not smooth which introduces discontinuities into the flow which result in further noise generation.
Further, the AeroClick vent and other prior art devices that are of a substantially cylindrical in-line configuration, the exhaled gas must thus be forced a relatively large distance (typically around 60 mm) before reaching the outlet to the atmosphere. This reduces CO2 washout efficiency, as noted above, and requires additional patient effort to force the gas against the direction of flow coming from the flow generator.
It is an object of the present invention to substantially overcome or at least ameliorate the prior art disadvantages and, in particular, to reduce the noise generated by venting exhaled gases to the atmosphere.
Accordingly, in a first aspect, the present invention provides a connector comprising:
a mask end for connecting in fluid communication with the interior of a respiratory mask;
a supply conduit end disposed at an angle to the mask end for connecting in fluid communication with the outlet of a breathable gas supply conduit; and
a gas washout vent passage having an inlet adjacent to, or forming part of, the mask end in fluid communication with the interior of the respiratory mask and an outlet in fluid communication with the atmosphere, the outlet including an interior surface that forms a smooth prolongation with an adjacent exterior surface of the connector, the vent outlet is disposed on the side of the connector remote the mask end, has a generally part-annular cross section and is adapted to direct the washout gas in a direction substantially perpendicular to the longitudinal axis of the mask end and substantially parallel to the longitudinal axis of the supply conduit end towards the supply conduit end.
The supply conduit end is preferably substantially perpendicular to the mask end. The supply conduit end can also be angled at approximately 135 degrees to the mask end.
Preferably, the connector includes a body portion and a cap portion, said body portion including said interior surface. The cap portion preferably also includes an interior surface spaced apart from the body portion interior surface, said body portion interior surface and said cap portion interior surface defining said vent passage therebetween.
The cap portion is desirably detachable from the body portion. The cap portion and body portion are also desirably rigid and fixed relative to each other when attached. The exterior of the body portion preferably includes grooves or ridges adapted to engage ridges or grooves respectively on the interior of the cap portion to attach the cap portion to the body portion. One of the body portion or cap portion preferably also includes a spacer extending between said cap portion interior surface and said body portion exterior surface.
In one form, the vent passage inlet is formed in the body portion adjacent to and downstream of the mask end, relative to the washout gas flow, and is in fluid communication with the mask interior via the body portion.
In another form, the vent passage inlet comprises part of the mask end and is in direct fluid communication with the mask interior.
The vent passage preferably comprises an inlet portion of relatively large cross-sectional area adjacent the vent passage inlet and an outlet portion of relatively small cross-sectional area adjacent the vent passage outlet.
The vent passage desirably comprises an inlet portion of constant cross-section, a relatively long outlet portion of constant cross-section and a relatively short transition portion of smoothly reducing cross-section extending from the inlet portion to the outlet portion. This shape reduces turbulence and affords a pressure drop from the interior of the mask to the outlet of the vent passage which reduces the pressure gradient at the outlet of the vent passage and, thus, reduces the noise generated.
The vent passage can also include internal ribs and/or an internal tortuous path to increase the pressure drop, if required.
The body portion is preferably of generally part toroidal shape. The cap portion is preferably of complimentary shape to a portion of the exterior of the body portion.
The vent passage preferably curves around the exterior of the body portion.
The connector desirably includes a swivel joiner at its supply conduit end, the exterior of the swivel joiner forming all, or a part, of said connector exterior surface.
In one form, the supply conduit end of the connector forms a smooth prolongation with the supply conduit. The supply conduit end and the supply conduit desirably have a substantially equal external diameter.
In another form, the swivel joiner forms a smooth prolongation with the supply conduit. The swivel joiner and the supply conduit having a substantially equal external diameter. The swivel joiner preferably includes an end of reduced external diameter adapted to be received within the interior of the supply conduit.
In a second aspect, the present invention provides a respiratory mask comprising:
a mask shell defining an interior of the respiratory mask;
a mask inlet for connecting in fluid communication with the outlet of a breathable gas supply conduit; and
a gas washout vent passage having an inlet forming part of the mask shell and in fluid communication with the interior of the respiratory mask and an outlet in fluid communication with the atmosphere, the outlet including an interior surface that forms a smooth prolongation with an adjacent exterior surface of the mask shell, the vent outlet is disposed on the side of the mask remote the mask interior and is adapted to direct the washout gas in a direction substantially parallel to the longitudinal axis of the mask inlet and away from the mask inlet.
Preferably, the mask shell includes a body portion and a cap portion, said body portion including said interior surface. The cap portion preferably also includes an interior surface spaced apart from the body portion interior surface, said body portion interior surface and said cap portion interior surface defining said vent passage therebetween.
The cap portion is desirably detachable from the body portion. The cap portion and body portion are also desirably rigid and fixed relative to each other when attached. The exterior of the body portion preferably includes grooves or ridges adapted to engage ridges or grooves respectively on the interior of the cap portion to attach the cap portion to the body portion. One of the body portion or cap portion preferably also includes a spacer extending between the interior surface of the cap portion and the exterior surface of the body portion.
The vent passage preferably comprises an inlet portion of a relatively large cross-sectional area adjacent the vent passage inlet and an outlet portion of a relatively small cross-sectional area adjacent the vent passage outlet.
The vent passage desirably comprises a relatively long inlet portion of constant cross-section, a relatively long outlet portion of constant cross-section and a transition portion of smoothly reducing cross-section extending from the inlet portion to the outlet portion.
The vent passage preferably substantially follows the shape of the exterior of the body portion.